This invention is in the field of medical devices and techniques for treating and healing open pressure sores, decubitus ulcers, venous ulcers and other wounds and more specifically for encouraging growth, regeneration and expansion of skin to cover such open wounds.
Pressure sores or decubitus ulcers are frequently encountered clinical problems. High risk patients are the elderly, diabetics, those with spinal cord injuries and patients requiring prolonged bed rest. In patients at high risk, prolonged pressure may lead to gangrenous changes. In diabetic patients foot problems are common and result in extensive hospitalization, disfiguring surgery, lifetime disability and diminished quality of life. In 1987 at least 56,000 diabetic individuals had at least one major limb amputation. In five years 50% will lose the second limb. The financial burden of amputation is enormous. Complications from foot problems are the cause of 20% of all diabetic admissions to hospitals. Approximately 10% of the diabetic population (5-10 million people) will be affected at some time in their lives with decubitus ulcers and foot problems.
A pressure ulcer usually develops when soft tissue is compressed between a bony prominence and a firm surface. When this pressure is above 32 mm Hg blood capillaries close. If this pressure is applied long enough the vessels thrombose. This development occludes blood flow, deprives tissue of oxygen, nutrients and waste removal paths, and leads to cell death or gangrene.
In the foot pressure ulcers are usually seen on the heel, metatarsal head, lateral border of the foot, midfoot, ankle and digits. Ulcers located on the heel and in the midfoot region are particularly resistant to successful treatment, midfoot ulcers having an amputation rate of 39% versus 6.8% in forefoot ulcers.
Pressure ulcers are also a serious and common complication of immobile elderly persons and patients with cerebral injuries such as paraplegics, quadraplegics, multiple sclerosis and strokes. The incidence of pressure ulcers in the elderly is 3% to 29% in acute care hospitals and nursing homes. Quadraplegics have an incidence of 60%. The cost of pressure ulcer treatment is substantial; estimates range from $4,000. to $40,000. per pressure ulcer. A pressure ulcer develops as a result of prolonged pressure on the bony prominences of the sacrum, trochanter and ischium.
Venous ulcers of the lower extremities afflict 1% of the general population and 3.5% of persons over 65 years of age, with a recurrence rate approaching 70%. Venous ulcers result from disorders of the deep venous system. When forward flow of venous blood is significantly disturbed or impaired, venous dysfunction ensues which result in increased hydrostatic pressure, venous hypertension, edema and ultimately, dermal ulceration. Venous ulcers are commonly found on the medial aspect of the leg.
Treatment of an ulcer includes removal of pressure on the ulcer, application of appropriate local dressings, medication and removal of necrotic tissue. Alternative approaches include topical growth factors and skin replacement. A recent study found poor healing to be a contributing cause in 81% of amputations in diabetic patients. The National Center for Health Statistics indicates an average of 20 inpatient days for persons hospitalized with skin ulcers.
Pressure ulcers or venous ulcers are difficult to heal. These ulcers are not surgical or incisional wounds; they require skin replacement. A surgical or incisional wound is made in normal healthy tissue, where the tissue is not contaminated, there is no underlying disease process, and the skin is easily stretchable. An ulcerative wound is always contaminated and often infected. There is an underlying disease process that causes the ulcer. Typically there are arterial, venous, lymphatic and neurologic problems and tissues are immuno-compromised by blood diseases or diabetes. Ulcerated tissues are fixed and rigid and often lie on and are adherent to the bone, tendon or joint.
Pressure ulcers are graded by the degree of damage to tissue observed. A stage III and stage IV pressure ulcer involves full thickness skin loss exposing subcutaneous tissue and underlying fascia. Stage IV pressure ulcers involve muscle, bone or supporting structures. These lesions with a deficiency of skin are treated by methods that encourage healing and closure of the defect. In some instances it is not possible to obtain complete coverage of the lesion. In any event healing by natural methods, growth factors or skin grafts results in a thin fragile layer of epidermal skin cover that is less well suited to the rigors of everyday life and has a tendency to breakdown.
The skin of the body has unique characteristics depending upon its location. The skin of the foot differs from facial skin. The skin of the foot is significantly thicker, adherent to the underlying tissues and supplied with elastic cushions of adipose tissue. It is so specialized to withstand the forces that act upon it that it is virtually irreplaceable. Skin grafts and flaps derived from other locations have difficulty tolerating the pressure and friction involved in the function of the foot. Skin grafts and growth factors basically replace part of the epidermis. They do not replace the dermis of the skin in which resides an elaborate vascular network and specialized arteriovenous shunts; the dermis is responsible for the ability of the skin to withstand the pressures and traumas of daily living.
The ideal wound closure would be one that can be closed at the local site with full thickness skin (epidermis and dermis). In most pressure ulcers and venous ulcers it is not possible to approximate the skin edges due to the size of the wound. Attempts to pull skin together under tension with the use of sutures results in strangulation of the blood supply of the sutured skin or the tearing of the suture through the skin.